Tearfund

TearFund is a large Christian charity with an international anti-​poverty agenda. They focus on five main areas: HIV, disaster response, challenging injustice, environmental action and helping with the basics (water, sanitation etc). Most if not all of their work is undertaken in less developed countries.
They’re a large charity, raising over £63m in ²⁰⁰⁷⁄₂₀₀₈. However despite their size I don’t think many people have heard of them — largely because a lot of their fund-​raising is done through local churches, typically evangelical ones (I think the ‘tear’ bit originally stood for The Evangleical Alliance Relief fund).
More information is available from their website (see link above) but TearFund is a very worthy cause and certainly one that enjoys our unreserved support.